We know that sleep is integral to how we function day to day – a sleepy brain makes for a sleepy body. But you may not realize just how much sleep impacts your body when you are chronically pushing bed time back in favour of getting more stuff done. Sleep is comprised of two different types, rapid eye movement (REM) and non-rapid eye movement (NREM). NREM can be further divided into 4 stages that are determined by the wakefulness of our brain and body, which in turn determines what important physiological processes happen during those stages. The most important NREM sleep are stages 3 and 4, lumped together into what we refer to as “slow wave sleep” (SWS). The amount of time per night spent in SWS is highly correlated with how rested we feel.

Here are some physiological processes that occur during SWS and the functional effects that we experience during the day:

Clearance of metabolic wastes from the brain – your brain cells don’t have the same type of blood supply as the rest of your body. This means that delivery of nutrients and removal of waste must happen through specialized pathways. During SWS your brain cells shrink by 60% allowing cerebrospinal fluid to wash over your brain cells clearing them of metabolic wastes accrued during the day (Xie et al. 2012). Our brain accounts for about 2% of our body mass but uses 20-25% of our daily energy expenditure. So, it’s working hard and needs that waste removed to allow for a clear head.

Appetite regulation – Leptin and grehlin, the hormones responsible for metabolic fuel storage and signaling hunger/satiety are regulated during SWS.

Functional outcomes: Without adequate sleep, we are likely to consume up to 24% more calories (Spiegel et a. 2004) – and not just because we’re awake more hours or have lower willpower! People who chronically don’t get enough sleep are more likely to be overweight (Taheri et al. 2004) and have a higher risk of diabetes (Gotlieb & Punjabi, 2005).

Autonomic Nervous System shift – SWS is when the autonomic nervous system is most in favour of parasympathetic activity. Because parasympathetic activity is so critical in physiological stress regulation and arousal of our body’s systems, SWS is when our organs and body’s systems finally get the rest and recovery they need to stay healthy. SWS also has a negative relationship with cortisol. So, increased cortisol (stress) = decreased SWS, and decreased SWS = increased cortisol (stress). Cortisol has wide ranging health effects when it is chronically elevated including immunosuppression, muscle atrophy, fat deposition, cognitive dysfunction, and brain atrophy.

Anabolic hormone release – Growth hormones are released during SWS. If you’re working with clients who are struggling to see training gains, ask them about their sleep habits. This is especially important for people coming back from an injury. Growth factors help speed healing. And, with the anti-inflammatory effects of SWS, the chronic problems like tendonitis may also be improved with SWS.

What advice can you give your clients to help them get better sleep? First, exercise (especially aerobic) has a strong positive relationship with sleep quality (Driver, 2000). Here are some guidelines for good sleep habits and other tips for improving sleep quality:

Aim for 8 hours (7.5 at the minimum)

Get at least one hour before midnight (SWS happens early in the night)

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